Fluid-flow machines of the abovementioned generic type are designed as rotary machines and have moving-blade elements along their axis of rotation, the free moving-blade ends of which face the inner wall of the fluid-flow casing in a freely movable manner. In the case of rotary machines through which the medium to be compressed flows axially relative to the rotor axis, guide-blade plates are normally attached firmly on one side to the inner wall of the casing of the rotary machine and their free end stands freely opposite corresponding contours on the rotor shaft. An essential aspect in the optimization of the compression efficiency or the turbine efficiency of such rotary machines is the reduction of leakage flows, i.e. of flow components, of the compressible medium flowing through the rotary machine, which pass through between the moving-blade ends or guide-blade ends and the contours opposite said ends. So-called labyrinth seals are used in order to reduce or avoid such leakage flows, these labyrinth seals comprising a multiplicity of intermeshing contours, which are able to seal, in a virtually gastight manner, the intermediate spaces between the rotating parts and the fixed casing parts together with guide blade. Thus the leakage flow can be reduced considerably when using labyrinth seals by virtue of the fact that the labyrinth seals themselves are provided with a multiplicity of individual sealing lips, but the disadvantage attached to this form of seal is that, the more labyrinth seals are provided in the interior of a rotary machine and these seals comprise a multiplicity of individual sealing lips, the greater become the frictional forces which, for example, act peripherally from outside on the rotating moving blades, as a result of which the mechanical loading of the rotating parts inside a rotary machine is increased. In addition, it is only rarely possible to accommodate a sufficient number of labyrinth elements for a high sealing effect.
Another solution for the reduction of leakage flows has been pursued in radial-compressor arrangements.
FIG. 2a shows a cross section through a radial compressor, which has a central rotor shaft 5, which is arranged in the interior of the casing 4 of the radial compressor. Connected to the rotor shaft 5 is a nozzle-like contour 11, through which, in the course of the rotation, preferably air is driven from inside to outside through the nozzle opening 12 by the centrifugal acceleration. Provided opposite the nozzle opening 12 of the contour 11 inside the casing 4 is an outlet opening 13, through which the compressed air leaves the radial compressor. In order to prevent leakage flows from escaping between the contour 11 and the inner casing 4 through the intermediate spaces 14, no labyrinth seals are provided, as in the case described above for axial compressors, but rather the fixed casing is deliberately spaced apart from the rotating contour 11 by a gap, so that a leakage flow could occur in principle. However, in order to reduce the leakage flow despite the existing gap, ribs 15 raised above the contour 11 are attached to the outside of the contour 11 (in this respect see FIG. 2d, from which a sectional drawing along section line A--A is depicted in developed form), and these ribs 15, on account of their radial movement, induce an annular flow in the intermediate spaces 14, and this annular flow creates inside the intermediate spaces 14 static pressure conditions which correspond to the pressure conditions which prevail in the region of the connecting gaps within the main flow. Due to such a pressure balance between the interior of the intermediate spaces 14 and the main flow, any leakage flows largely cease.
Although a certain proportion of rotary energy must be invested in the generation of an annular flow required in the interior of the intermediate spaces 14, tests and measurements show that an expenditure of energy in this respect is below the energy which is mainly lost through leakage when using labyrinth seals.